Stop using pyside2==5.12.4 to avoid weird error
Had this problem with pyside2==5.12.4
```
$ pytest -v tests
INTERNALERROR> Traceback (most recent call last):
INTERNALERROR> File "/home/travis/miniconda/envs/test/lib/python2.7/site-packages/_pytest/main.py", line 202, in wrap_session
INTERNALERROR> config._do_configure()
INTERNALERROR> File "/home/travis/miniconda/envs/test/lib/python2.7/site-packages/_pytest/config/__init__.py", line 671, in _do_configure
INTERNALERROR> self.hook.pytest_configure.call_historic(kwargs=dict(config=self))
INTERNALERROR> File "/home/travis/miniconda/envs/test/lib/python2.7/site-packages/pluggy/hooks.py", line 311, in call_historic
INTERNALERROR> res = self._hookexec(self, self.get_hookimpls(), kwargs)
INTERNALERROR> File "/home/travis/miniconda/envs/test/lib/python2.7/site-packages/pluggy/manager.py", line 87, in _hookexec
INTERNALERROR> return self._inner_hookexec(hook, methods, kwargs)
INTERNALERROR> File "/home/travis/miniconda/envs/test/lib/python2.7/site-packages/pluggy/manager.py", line 81, in <lambda>
INTERNALERROR> firstresult=hook.spec.opts.get("firstresult") if hook.spec else False,
INTERNALERROR> File "/home/travis/miniconda/envs/test/lib/python2.7/site-packages/pluggy/callers.py", line 208, in _multicall
INTERNALERROR> return outcome.get_result()
INTERNALERROR> File "/home/travis/miniconda/envs/test/lib/python2.7/site-packages/pluggy/callers.py", line 81, in get_result
INTERNALERROR> _reraise(*ex) # noqa
INTERNALERROR> File "/home/travis/miniconda/envs/test/lib/python2.7/site-packages/pluggy/callers.py", line 187, in _multicall
INTERNALERROR> res = hook_impl.function(*args)
INTERNALERROR> File "/home/travis/miniconda/envs/test/lib/python2.7/site-packages/pytestqt/plugin.py", line 228, in pytest_configure
INTERNALERROR> QtBot._inject_qtest_methods()
INTERNALERROR> File "/home/travis/miniconda/envs/test/lib/python2.7/site-packages/pytestqt/qtbot.py", line 645, in _inject_qtest_methods
INTERNALERROR> method = create_qtest_proxy_method(method_name)
INTERNALERROR> File "/home/travis/miniconda/envs/test/lib/python2.7/site-packages/pytestqt/qtbot.py", line 624, in create_qtest_proxy_method
INTERNALERROR> functools.update_wrapper(result, qtest_method)
INTERNALERROR> File "/home/travis/miniconda/envs/test/lib/python2.7/functools.py", line 32, in update_wrapper
INTERNALERROR> for attr in assigned:
INTERNALERROR> File "/home/travis/miniconda/envs/test/lib/python2.7/site-packages/shiboken2/files.dir/shibokensupport/signature/parser.py", line 286, in pyside_type_init
INTERNALERROR> update_mapping()
INTERNALERROR> File "/home/travis/miniconda/envs/test/lib/python2.7/site-packages/shiboken2/files.dir/shibokensupport/signature/mapping.py", line 233, in update
INTERNALERROR> candidates = list(mod_name for mod_name in sys.modules
INTERNALERROR> File "/home/travis/miniconda/envs/test/lib/python2.7/site-packages/shiboken2/files.dir/shibokensupport/signature/mapping.py", line 233, in <genexpr>
INTERNALERROR> candidates = list(mod_name for mod_name in sys.modules
INTERNALERROR> RuntimeError: dictionary changed size during iteration
The command "pytest -v tests" exited with 3.
```
Kentaro Wada